Plastic parts often require grooves or undercuts about an internal bore to accommodate snap fitting parts. One example is a snap-cap used to close a plastic container. The existing technique used to provide undercuts or grooves in such molded parts is to use collapsable core pins. These core pins, usually in the form of a split collet, include cam mechanisms permitting the core pin to be expanded once it is inserted between the mold halves. Plastic is injected between the mold halves and around the core pin to form the molded part. The cam mechanism is again actuated so that the split collet returns to its pre-expanded state so that the core pin can be removed from the mold.
While use of a split collet type core pin may adequately provide grooves or undercuts of relatively large diameter, it is difficult to construct a cam actuated core pin mechanism of this type for grooves or undercuts of smaller diameter. Cam actuation of smaller components is cumbersome. Also, it is difficult to form small, precise parts using this technique.
It is desirable to provide a core pin mechanism which can be easily inserted into and removed from a mold and which permits the formation of a groove or undercut of relatively small size in the molded part.